Superoxide dismutases catalyze the decomposition of the superoxide radical, thus protecting aerobes from this radical and other cytotoxic species formed during the reduction of xxygen to water. There are three forms of superoxide dimutases: manganese-, iron-, and copper-and-zinc-containing enzymes. prokaryotes contain manaanese or iron dismutases, or both. Copper-zinc dismutases are found in most eukaryote cytosols; eukaryote organelles contain the manganese enzyme. Why do certain species contain a certain type(s) of superoxide dismutase and other species another type(s)? The long range goal of this project is to identify the structural and the chemical properties of the three dismutase forms which make them particularly suited for the species and intracellular location in which they reside. The principal methodology is comparative amino acid sequence analysis. Current efforts are focused on the manganese dismutase from chicken liver mitochondria. Quantities of the enzyme suitable for structural analysis are being purified, and sequencing will be begun during the next budget year, May, 1980 - April, 1981. If time allows, enzyme purification and sequence work will also be initiated on the bacteriocuprein of Photobacterium leiognathi, an anomaly in the general scheme of dismutase phylogeny, because it is a copper-and-zinc enzyme which appears in a bacterium. Information about culturing the bacterium and details of a modified purification procedure will be obtained from Dr. Irwin Fridovich of the Duke University Biochemistry Department.